Method and Apparatus for Separation of Impurities from Liquid by Upflow Granular Media Filters

ABSTRACT

The present invention is a gravity continuously operating filtration system for separating impurities from liquids. The liquid flows upward through a bed of filter media in a vessel and filtered liquid (filtrate) is collected above the top of the bed. Dirtied filter media are withdrawn from the bottom of the vessel and returned to the vessel from the top. The dirtied filter media are first conveyed to a separation device by which the bulk of solids are separated from the filter media. The reject liquid from the separation device is discharged as waste. The filter media are then cleaned in a spiral wash path and are then returned back to the system. The described cleaning process is far more effective than other similar filtration systems. Majority of essential components are located outside of the vessel and are convenient to access for maintenance and inspection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This relates to a method, an apparatus, and a system for the separationof impurities from liquid. In particular, the invention relates to animproved method and an improved apparatus to filter, but not limited to,suspended solids, from a liquid.

2. Description of the Prior Art

The conventional method to remove suspended solids from a liquid is topass the liquid through a bed of granular media in a downward direction(i.e., from the top to the bottom.). When solids contacts with thegranular media, they are retained by them and are therefore removed fromthe liquid. A device like this is called filter. Once the media aresaturated with suspended solids, the filter must be shut down and thefiltration process will be stopped to regenerate the media. This processis called backwash. The backwash process typically consists ofdislodging solids by introducing a stream of air by itself or incombination with a stream of water in an opposite direction (i.e., fromthe bottom to the top) for a period of time (usually, a couple ofminutes) and then followed by a stream of water for an additional periodof time (usually, ten minutes or so). After the backwash, the filterneeds to be ripened for a period of time before it can be placed backinto the filtration again. The filter ripen period could take about onehour. The filtration, backwash, and filter ripen processes are repeatedto make up a complete production cycle.

The disadvantage of a conventional filtration system is that thefiltration process can not be continuous as the filer media has to beregenerated periodically. The normal filtration stops while the mediaare being regenerated. This procedure reduces the productivity of thesystem.

Another disadvantage of the conventional filtration system is that inorder to produce clean water continuously, at least one standby unit hasto be provided and turned on while the active unit is being backwashed.The installation of a standby unit increases the cost of such a systemunnecessarily.

Additional disadvantage of the conventional filtration system discussedabove is that a backwashing system has to be provided to perform thebackwash. A typical backwashing system includes an air supply system(usually include an air compressor(s) or blower(s)), backwash waterpump(s), and often backwash water supply/storage unit. The backwashingsystem adds extra expenses to the overall treatment system investment.

Continuous filtration devices as revealed in some prior acts addressedsome of aforementioned problems. An example is a countercurrentcontinuous filter as described in U.S. Pat. Nos. 4,126,546 and 4,197,201issued to Hjelmn{hacek over (e)}r and Larsson in 1978 and in 1980,respectively. In such a filter, the liquid is introduced from the bottomof a tank which containing a bed of sand and the cleaned liquid exitsfrom the top of the tank. The dirtied sand is transported through aconduit located in the center of the tank via an air-lift pump to awashing device situated above the sand bed. A filter like this addressedsome of problems associated with a conventional filter and it has beeninstalled in commercial scale around the world. However it has its ownserious drawbacks.

One major drawback of a filter described in U.S. Pat. Nos. 4,126,546 and4,197,201 is that the washing device is inadequate for cleaning thefilter media. The filter media is cleaned in a washing device which usesthe filtered water as the washing fluid. The effectiveness of thisprocess is relatively poor. The turbidity and concentration of suspendedsolids in the product water was high and could not meet the potablewater standard established by United States Environmental ProtectionAgency (USEPA). For instance, the turbidity in the filter effluent wasin the range of 0.1 to 0.5 nephelometric turbidity units (NTU) when sucha filter described above was used to produce drinking water (ParksonCorporation, Dynasand® Continuous Upflow Granular Media Filter Brochure,available online at www.parson.com accessed on Jun. 2, 2011). Thestandard established by USEPA is that the turbidity in the filtereffluent must be less than 0.3 NTU in 95 percent of daily samples. Toproduce water for safe human consumption, one must install two this kindof filters in serial as described in U.S. Pat. Nos. 6,426,005 B1 and5,843,308 (Parkson Corporation, Product Brochure—Dynasand® D2 AdvancedContinuous Backwash Filtration System Brochure, available online atwww.parson.com accessed on Jun. 2, 2011). Using dual stage of such afilter as disclosed in U.S. Pat. Nos. 6,426,005 B1 and 5,843,308severely limits its application in cases where high quality of water isrequired, such as potable water production, since such a system wouldrequire significantly higher investment and occupy doubled footprint.

Another drawback of a filter described in U.S. Pat. Nos. 4,126,546 and4,197,201 is that the air-lift mechanism is insufficient to break up thebinding between solids and filter media and results in elevated solidconcentration in the treated water. The solids are adsorbed on thefilter media and the bindings between the solids and filter media arepronounced and strong. Using a stream of air in such a filter is unableto effectively break up the binding between the solid and the filtermedia and therefore adequately clean the media. If the filter media arenot cleaned adequately, it could lose its filtering capacity and it hasto be cleaned more frequently in order to produce the water with thesame quality.

Still another drawback of a filter described in U.S. Pat. Nos. 4,126,546and 4,197,201 is that it is difficult to access the air-lift transportconduit for inspection, maintenance, or repair. The transport conduit islocated centrally inside the tank. The transport conduit is subject toclogging and blockage due to the nature of the dirtied filter media.Since the transport conduit is located inside the tank which is filledwith the filter media, the filter media must be evacuated before one caninspect, maintain, or repair the transport conduit which increases thedowntime and requires more labor.

One additional drawback of a filter described in U.S. Pat. Nos.4,126,546 and 4,197,201 is that localized fluidization in the filer bedis inevitable as compressed air is utilized as the driving force totransport the dirtied sand for cleaning. Although an air capture devicewas included, a portion of the air would inevitably escape into the tankand cause localized fluidization of the filter media. Fluidization in afilter is undesirable as it could reduce the filtration efficiency ofthe filter media and results in higher concentration of solids andturbidity in the effluent.

In general, a continuous-backwashing filter as disclosed in U.S. Pat.Nos. 4,126,546 and 4,197,201 is economically infeasible in itsapplication in high quality water production such as the potable waterproduction. Its application is limited in situations where the waterquality requirement is low. Two filters must be installed in series inorder to produce water which is safe for human consumption. A filterlike the one disclosed in U.S. Pat. Nos. 4,126,546 and 4,197,201 isdifficult to maintain and repair. Using compressed air as the means oftransportation makes the system complicated. A filter like this dependson air as the transport mechanism for regeneration of the filter mediawhich causes localized fluidization of the filter media. Similarcontinuous filters are also disclosed in U.S. Pat. Nos. 4,720,347,5,277,829, and 5,746,913 issued to Berne, Ward, and Chang in 1988, 1994,and 1998, respectively. They have similar disadvantages as discussedabove.

Accordingly, it is an object of the present invention to provide acontinuous filtration system which utilizes the whole bed of filtermedia by counter-current flow, between the filter media and the liquid,for the treatment of liquid.

It is another object of the present invention to provide an improvedcontinuous filtration system which can effectively regenerate the filtermedia and enhance the quality of filtrate for the treatment of liquid.

These objects will become more obvious after reading the detaileddescription referenced to the drawing.

SUMMARY OF THE PRESENT INVENTION

In accordance with the present invention, there is provided acounter-current, continuous filtration system that is designed toseparate impurities from liquid. The filtration system of the inventioncomprises a tank that is filled with filter media and the influent issupplied into a bed of filter media through a series of distributionradials from the lower part of the tank. As the influent flows upwardlythrough the filter media bed, the impurities are intercepted by andretained on filter media and therefore removed from the liquid. Thetreated liquid exits at the top of the tank. The dirtied filter mediaare withdrawn from the base of the tank via a transport device which islocated outside the tank. The solids and filter media are subsequentlyseparated via and a separation. The reject from the separation device isdischarged as waste. The filter media are further washed using thefiltrate and the cleaned filter media return back to the bed from thetop.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, a preferred embodiment of filter apparatus ofthis invention is presented.

A tank 201 contains a filter bed 205 consisting of loose, granularfilter media, preferably of uniform grain size. The tank 201 is definedby vertical walls 230 and conical or inclined walls 228 which form afunnel-shaped bottom. The filter media can consist of e.g. sand, sandand gravel, or any granular material having an absorptive surfacestructure (sand is used as the filter media as illustrative purposehere). Liquid 225, which can be water or any other liquids need to befiltered, enters through an inlet pipe 202. The inlet pipe 202 connectsto a series of distribution radials (the radial rack) 204 whichintroduces the liquid 225 into the filter bed 205. The radial rack 204is located concentrically at the vertical base of the filter bed and itensures the liquid 225 is equally distributed within the filter bed 205.A funnel 206 is placed upside down and is connected in the center of theseries of the influent distribution radials 204 through a funnelconnector 229. The funnel 206 prevents the short-circuiting of theinfluent liquid 225. The liquid 225 flows upwardly while the filter bed205 moves downwardly to the base of the tank 201. Solids in the liquid225 are effectively removed by the filter media during thiscounter-current movement. The filtrate (i.e., the filtered liquid) 223exits from the top of the filter bed 205 through an effluent weir 217.The weir 217 is connected to an exit conduit 218 which transports thefiltrate 223 out of the tank 201.

During the counter-current movement, the most dirtied liquid iscontacted with the filter media at the vertical bottom of the filter bed205 and the filter media sand consequently becomes most dirty. Thecounter-current mode of filtration takes advantages of all availablefilter media and is very effective. The dirtied sand 220 slides to thebottom of the tank 203 with the aid of the funnel 206. The bottom 203 isconnected to a transport conduit 207. A pump 208 is connected to thetransport conduit 207 to withdraw the dirtied sand 220 out of the tank201. The solids which are bound with the sand are partially dislodged bythe agitation introduced by the pump 208. The mixture of sand and solids231 exits the pump 208 through the discharge pipe 226. The mixture ofsand and solids 231 then goes through an in-line shear 209. The in-lineshear 209 breaks up the binding between the solids and sand andcompletely dislodge the solids from the sand. The binding between thesolids and sands could be strong and an extreme example of cakedaggregate of solids on the filter media is often referred as mud ball.The mud ball reduces the filtrate quality by lowering the efficiency ofthe filter media. The life span of the filter media is also shortened bythe presence of mud ball. The in-line shear effectively breaks up thebinding between the solids and sands and dramatically increases thesubsequent cleaning efficiency of the filter media.

The mixture of sands and solids 231 after exiting the in-line shear isconveyed to a hydrocyclone 232. In the hydrocyclone, the sands 221 andthe dirtied water 222 in the mixture 231 are effectively separated underthe centrifugal force. The mixture 231 enters the hydrocyclone 232 viaan inlet 211 tangentially. The mixture 231 spins in the inlet 211 andthe heavier sands 221 are thrown toward the wall of the chamber. Thesands 221 continue on a downward spiral path to the bottom apex 233 andexit the hydrocyclone 232 via a conduit 215. The less dense fraction ofthe mixture, the dirtied water (hydrocyclone reject) 222, moves in theopposite direction, spiraling upward on the axis of the hydrocyclone andexits the hydrocyclone 232 through an outlet 212. It is then dischargedvia a reject discharge conduit 213 as waste.

The sands 221 exited the hydrocyclone 232 is further cleaned in a sandwasher 214. The sands 221 arrives the upper end of the washer 214 formedby walls 227 and flows downwardly through a spiral wash path 234. Thespiral wash path is submerged in the filtrate 223 in the tank 201 andhence there is a constant upward movement of the filtrate in the washpath 234. The sands 221 meets with the filtrate constantly in thecounter-current motion and is cleaned once it reaches the end of thewash path 234.

The sands 221 returns back to the filter media bed 205 as cleaned filtermedia 224. The wash wastewater 235 exits the washer 214 through a weir216 via a discharge conduit 219. The wash wastewater discharge conduit219 is connected to the inlet 202. The wash water 235 is combined withthe influent 225 and is recycled back to the tank 201. The weir 216 ispositioned below the filtrate weir 217 and this ensures that there is aconstant flow of water through the weir 216. The dirtied sand can bewashed continuously or on an intermittent basis depending oncircumstances.

Although a preferred embodiment of this invention has been describedrelative to the drawing, it should be understood that the embodiment ofthe invention described above are merely illustrative and othermodification may be made by those skilled in the art. For example, othergranular materials could be used as the filter media instead of sand asdescribed. A magnetic separator could be used as the separation deviceinstead of hydrocyclone when magnetite is used as the filter media. Thewash wastewater could be returned to the bottom of the tank instead ofreturning to the influent. These and a variety of other modification maybe made within the scope of the invention, which is defined by theappended claims.

1. In a method of separating impurities from a liquid by introducingsaid liquid upwardly across a bed of particular filter media, duringwhich said filter media separates impurities from said liquid andbecomes dirtied thereby, and thus said filtered liquid is collectedabove said bed, the improvement comprising cleaning the thus dirtiedfilter media without interrupting said filtration process by: providinga transport device to transport filter media from a lower portion ofsaid filter bed to a position above upper surface of said bed, thereinturbulence introduced by said transport device performing the firstwashing of said dirtied filter media; directing said dirtied filtermedia to a separation device to separate said impurities from saiddirtied filter media and therein performing a further washing of saidfilter media by said separation device, and discharging said filtermedia from said separation device, such that said filter media fallsdownwardly toward said upper surface of said bed; and directing saidseparated filter media downwardly toward said upper surface of said bedthrough a spiral path and performing a further washing of said filtermedia by means of filtered liquid, after which thus multiple-time-washedfilter media falls onto said surface of said bed; whereby saidimpurities will be effectively separated from said liquid, and saidfilter media will be effectively cleaned and returned back to saidfilter bed.
 2. A method claimed in claim 1, wherein portion of saiddirtied wash liquid is returned to said filtration process.
 3. A methodclaimed in claim 1, comprising performing said media washingintermittently or continuously.
 4. A method claimed in claim 1, whereinsaid separation device includes one or more of the following: ahydrocyclone or magnetic separator.
 5. In an apparatus of separatingimpurities from a liquid by introducing said liquid upwardly across abed of particular filter media, during which said filter media separatesimpurities from said liquid and becomes dirtied thereby, and thus saidfiltered liquid is collected above said bed, the improvement comprisingcleaning thus said dirtied filter media without interrupting saidfiltration process by: providing a transport device to transport saidfilter media from a lower portion of said filter bed to a position aboveupper surface of said bed, therein turbulence introduced by saidtransport device performing the first washing of said dirtied filtermedia; directing said dirtied filter media to a separation device toseparate said impurities from said dirtied filter media and thereinperforming a further washing of said filter media by said separationdevice, and discharging said filter media from said separation device,such that said filter media falls downwardly toward said upper surfaceof said bed; and directing said separated filter media downwardly towardsaid upper surface of said bed through a spiral path and performing afurther washing of said filter media by means of filtered liquid, afterwhich thus multiple-time-washed filter media falls onto said surface ofsaid bed; whereby said impurities will be effectively separated fromsaid liquid, and said filter media will be effectively cleaned andreturned back to said filter bed.
 6. An apparatus claimed in claim 5,wherein portion of said dirtied wash liquid is returned to thefiltration process.
 7. An apparatus claimed in claim 5, comprisingperforming said media washing intermittently or continuously.
 8. Anapparatus claimed in claim 5, wherein said separation device includesone or more of the following: a hydrocyclone or magnetic separator.